1. Field of the Invention
The invention relates generally to blue-light sources used to polymerize dental restoration composite materials and specifically to light-curing systems that use xenon arc lamps coupled through liquid-filled light guides to a wand.
2. Description of the Prior Art
Up until very recently, dentists universally used catalytically cured resins to fill cavities and restore teeth. Now most such restorative materials are light-cured, wherein exposure to intense light is used to polymerize and harden the fillings. The most energetic light wavelength to use is ultraviolet (UV) light because each UV-photon packs far more energy than do photons of light having longer wavelengths. But UV-light is associated with skin damage and can be hazardous to both dentist and patient alike.
Robert D. Maurer, et al., describes such light-cured materials and the hazards associated with exposure to ultraviolet and other intense light sources in U.S. Pat. No 5,182,588, issued Jan. 26, 1993. Glasses with filter coatings are proposed that absorb UV-light and blue-light to protect the dentist's eyes. This, of course, does nothing to protect the patient's exposed skin or the face and hands of the dentist.
The use of UV-light to polymerize dental composite materials proved to be too hazardous, so now blue-light only systems are used that provide as good, if not superior performance. Several manufacturers of the blue-light cured dental composite materials now exist. These roughly fall into two categories, ones that nominally cure at 430 nanometer light-wavelength, and ones that cure at about 470 nanometers.
A typical short arc lamp comprises an anode and a sharp-tipped cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains xenon gas pressurized to several atmospheres. U.S. Pat. No. 5,721,465, issued Feb. 24, 1998, to Roy D. Roberts, describes such a typical short-arc lamp. Such Patent is incorporated herein by reference. A typical xenon short-arc lamp is marketed by ILC Technology (Sunnyvale, Calif.) under the CERMAX.TM. trademark.
Bare, unfiltered xenon arc lamps put out a wide spectrum of light values. Too wide, in fact, for their use in blue-light dental composite material curing systems. Both the 430 and 470 nanometer wavelengths of light will be found in the output of a xenon lamp, and these can be used for polymerization. But many other wavelengths are also produced that must be absorbed as heat by the patients and their teeth. These other wavelengths contribute nothing to the polymerization. The absorbed heat can irritate or worry the patient, and therefore complicate the dentist's job.
A portable high-power arc-lamp system for composite curing and teeth whitening is described by John Cipolla in U.S. Pat. No 5,879,159, issued Mar. 9, 1999, (Cipolla '159). FIG. 2 of such patent shows the spectral output of an optical blue-green color bandpass filter (127) that is used, i.e., 430-500 nanometers. Such color bandpass filter is mounted external to the lamp and resembles a monocle on a holder. The unfiltered spectral output of a xenon short arc lamp is illustrated in FIG. 3 of Cipolla 159. Such lamps produce significant amounts of infrared energy, so Cipolla suggests that a separate dichroic filter can be inserted between the reflector and light guide to absorb and dissipate the infrared wavelengths.
As it turns out, so much infrared light is output by the xenon arc lamp in prior art blue-light curing systems that the color bandpass filters alone can not handle the heat loads. An infrared pre-filter is needed to spread the heat deposited in the filters between two such filters. Otherwise, the glass on which the filter coatings are deposited will heat up to several hundred degrees Celsius and fracture. As can be expected, these filters add extra cost to the manufacture of such systems.
Another problem in prior art polymerization systems is controlling the dosage of the blue-light radiation applied to polymerize the composite materials. Volume 2, number 2, of "inciDENTALs", the Journal for the Dental Assistant and Receptionist, .COPYRGT. 1998, states that the curing lights now in use have output energies that diminish over time. So stand-alone light-meters are suggested to periodically test the intensity of a dentist's curing light. Such suggests that if a reading of "200-300" is obtained, then the recommended curing time should be increased. If the reading is under "200", then the lamp is bad and should be repaired or replaced. This caution indicates that some procedures may, in fact, under-cure or over-cure the dental composite materials because the dosage rate can vary unbeknownst to the dentist.